High pressure pump

Abstract

A positive displacement pump for pumping a fluid mastic comprises a plurality of cylinders each having a piston arranged for reciprocal motion within the cylinder. Movement of the piston in a first direction draws the fluid into the cylinder and movement in a second, opposite direction pumps the fluid out of the cylinder. A variable speed electric motor is drivingly coupled to a cam arrangement providing a reciprocating drive to the pistons. The cam arrangement comprises cams shaped and arranged to drive each piston in the first direction over less than half of a rotational cycle and to drive each piston in the second direction over the remainder of the rotational cycle. The cams are arranged to drive the pistons out of phase with one another.

1 . A positive displacement pump suitable for pumping a fluid mastic, the pump comprising:
 at least three cylinders wherein each cylinder each has a piston arranged for reciprocal motion within the cylinder, whereby movement of the piston in a first direction draws the fluid into the cylinder and movement in a second, opposite direction pumps the fluid out of the cylinder; and   a variable speed electric motor drivingly coupled to a cam arrangement providing a reciprocating drive to the pistons,   wherein the cam arrangement comprises cams shaped and arranged to drive each piston in the first direction over less than half of a rotational cycle and to drive each piston in the second direction over the remainder of the rotational cycle, wherein the cam arrangement has one cam for each piston, wherein each cam has a main surface and a return surface, wherein the main surface is configured to offset from the return surface along a direction of an axis of a cam shaft ,   wherein the cams are arranged to drive the pistons out of phase with one another; and   wherein the cams are arranged to drive the pistons such that, at any position of the rotational cycle more than half of the pistons are being driven in the second direction.   
     
     
         2 . The positive displacement pump of  claim 1 , wherein the cams are arranged such that a change in the direction of movement of any piston from the second direction to the first direction occurs at an angle of less than 5 degrees of rotation of the cams after another piston has changed direction from the first direction to the second direction, thereby providing that an increased number of pistons are pumping fluid prior to each change of direction of a piston from the second direction to the first direction. 
     
     
         3 . The positive displacement pump of  claim 2 , wherein the angle of less than 5 degrees of rotation of the cams is an angle of less than 2 degrees. 
     
     
         4 . The positive displacement pump of  claim 1  wherein the variable speed electric motor is an ac motor. 
     
     
         5 . The positive displacement pump of  claim 4 , wherein the ac motor has an inverter, the inverter having a closed loop vector drive control. 
     
     
         6 . The positive displacement pump of  claim 5 , wherein the ac motor has a shaft encoder providing a signal indicating a position of the rotor to the inverter. 
     
     
         7 . The positive displacement pump of  claim 6  wherein the ac motor includes a forced convection fan arranged to provide cooling air to windings of the motor. 
     
     
         8 . A positive displacement pump suitable for pumping a fluid mastic, the pump comprising:
 at least three cylinders wherein each cylinder has a piston arranged for reciprocal motion within the cylinder, whereby movement of the piston in a first direction draws the fluid into the cylinder and movement in a second, opposite direction pumps the fluid out of the cylinder; and   a variable speed electric motor drivingly coupled to a cam arrangement, wherein the cam arrangement comprises cams, wherein the cams are configured to provide a reciprocating drive to the pistons, wherein the cam arrangement has one cam for each piston, wherein each cam has a main surface and a return surface, wherein the main surface is configured to offset from the return surface along a direction of an axis of a cam shaft, wherein the electric has an inverter, the inverter having a closed loop vector drive control,   wherein the cams are arranged to drive the pistons such that, at any position of the rotational cycle more than half of the pistons are being driven in the second direction.   
     
     
         9 . The positive displacement pump of  claim 8 , wherein the variable speed electric motor is an ac motor comprising a shaft encoder configured to provide a signal indicating a position of the rotor to the inverter. 
     
     
         10 . The positive displacement pump of  claim 9  wherein the ac motor includes a forced convection fan arranged to provide cooling air to windings of the motor. 
     
     
         11 . The positive displacement pump of any of  claim 8 , wherein the cam arrangement comprises cams shaped and arranged to drive each piston in the first direction over less than half of a rotational cycle and to drive each piston in the second direction over the remainder of the rotational cycle, and
 wherein the cams are arranged to drive the pistons out of phase with one another.   
     
     
         12 . The positive displacement pump of  claim 11 , wherein the cams are arranged such that a change in the direction of movement of any piston from the second direction to the first direction occurs at an angle of less than 5 degrees of rotation of the cams after another piston has changed direction from the first direction to the second direction, thereby providing that an increased number of pistons are pumping fluid prior to each change of direction of a piston from the second direction to the first direction. 
     
     
         13 . The positive displacement pump of  claim 12  wherein the angle of less than 5 degrees of rotation of the cams is an angle of less than 2 degrees. 
     
     
         14 . The positive displacement pump of  claim 8 , wherein the cam arrangement includes a first cam and cam follower for each piston and a second cam and cam follower, 180° out of phase with the first cam and cam follower, wherein the first and second cam followers are connected to each other such that the distance between them is always the same, and the cam surfaces are shaped to ensure that the cam followers maintain contact with the respective cams at all times. 
     
     
         15 . The positive displacement pump of  claim 14 , wherein the cam followers are configured to maintain contact with their respective cams by springs. 
     
     
         16 . The positive displacement pump of  claim 8 , wherein the cams have constant velocity cam surface profiles.